The structure of acetylcholinesterase is being examined by physical methods and analysis of subunits and subunit composition. A fluorescence probe, pyrenebutanolmethylphosphofluoridate, has been syntheszed and its conjugation with acetylcholinesterase studied. This probe has enabled us to employ energy transfer and dynamic quenching to ascertain enzyme topology. Fluorescence polarization will be used to investigate segmental motion in the enzyme. Finally subunit structures of the head and tail units of acetylcholinesterase are being examined by methods of classical protein chemistry.